BLOCK: We begin with election technology. Tomorrow, almost everyone who goes to the polls will use electronic voting machines or have their ballots read by an optical scanner. Millions of people, tens of thousands of pieces of equipment, and there are bound to be problems. Computer experts say voting technology has gotten a lot better in the past few years. Still, there are concerns about security and reliability, as NPR's Pam Fessler reports.

PAM FESSLER, BYLINE: Already, there have been some complaints. The Republican National Committee last week sent a letter to six secretaries of state noting reports that some voting machines appeared to be flipping votes from Mitt Romney to Barack Obama. And today, a group of computer security experts raised red flags about New Jersey's plan to allow voters displaced by Superstorm Sandy to send in their ballots by email. Andrew Appel of Princeton University says Internet voting is insecure.

ANDREW APPEL: And email voting is the most insecure form of Internet voting. It's quite easy to fake an email return address.

FESSLER: And no way, he says, for New Jersey officials to know who's actually casting the electronic ballot. Still, overall, says Charles Stewart of MIT, things are looking pretty good this year when it comes to voting technology.

CHARLES STEWART: I'm very confident in general about the accuracy of the vote counts.

FESSLER: He notes that states have upgraded their voting equipment substantially since the 2000 voting debacle. And many problems with electronic voting machines have been worked out in recent years with better security measures and with more tech-savvy voters, election officials and poll workers.

STEWART: You know, when it comes out to the nightmare scenarios that I'm running through my mind, they're not about technology per se. But they're really about, you know, the low-tech problems of having a lot of paper left on the table at the end of Election Day.

FESSLER: Paper such as absentee and provisional ballots, which are much more prone to mistakes and legal challenges. Still, Stewart and others say there are reasons to worry about voting technology. While many jurisdictions have replaced their electronic voting equipment with paper-backed systems, that's not the case everywhere.

Larry Norden with the Brennan Center for Justice in New York notes that states such as Virginia and Pennsylvania still use paperless touch screen voting machines.

LARRY NORDEN: That makes it impossible to do a comparison of the paper records to the software totals. So to the extent that something goes wrong with those machines, there's always more of a concern in that because there's no backup paper record.

FESSLER: That also makes it difficult, he says, to do a meaningful recount, even if a state is crucial to the presidential race. Norden is also concerned about how all the voting machines purchased after 2000 will hold up, if not for tomorrow, then for the next election.

NORDEN: Many of them are getting old, and they're coming to the end of their lifespan.

FESSLER: Which he says typically is about 10 years. Charles Stewart of MIT says one thing voters can do to minimize problems tomorrow is to know how to use the equipment they have. Take that vote-flipping problem the RNC is so worried about. Stewart says it's a pretty rare occurrence but that voters should always carefully review the final screen before they cast their ballot.

If the wrong candidate's name appears, they should tell a poll worker right away so they can either fix the problem, move them to a new machine or find another way for them to vote. Pam Fessler, NPR News, Washington. Transcript provided by NPR, Copyright NPR.